The present invention relates to a ribbon shaped magnet material, a magnetic powder and a rare earth bonded magnet.
A bonded magnet prepared by bonding a magnetic powder with a bonding resin is used for motors and various actuators by taking advantage of its wide degree of freedom of configuration.
Magnet materials constituting the bonded magnet described above are manufactured by, for example, a quenching method using a quenching type ribbon manufacturing apparatus. The manufacturing method is called a single roll method when the quenching type ribbon manufacturing apparatus comprises a single cooling roll.
In the single roll method, a thin foil (ribbon) of a magnet material, or a quenched ribbon, is continuously formed by the steps comprising heating and melting a magnet material with a prescribed alloy composition, ejecting the molten liquid from a nozzle to allow it to collide with the circumference surface of a cooling roll rotating relative to the nozzle, and quenching and solidifying the molten liquid by allowing it to contact the circumference face. The quenched ribbon is pulverized into a magnetic powder, and a bonded magnet is manufactured using this magnetic powder.
The cooling roll used in the single roll method is generally composed of a copper alloy or an iron alloy. Some cooling rolls comprise metal or metal alloy surface layers formed by, for example, Cr plating on the circumference face of the cooling roll for improving durability.
However, since the circumference face of the cooling roll as described above is composed of a metal having a high heat conductivity, a difference in the cooling rate is caused between the roll contact surface (the surface at the side in contact with the circumference face of the cooling roll) and free surface (the surface opposed to the roll contact surface) of the quenched ribbon, resulting in a large difference of the microstructure (for example, the difference of the crystal grain size) between the two surfaces. Accordingly, the magnetic powders manufactured by pulverizing the ribbon involve heterogeneous magnetic characteristics among each lot of the magnetic powder. Therefore, satisfactory magnetic characteristics cannot be obtained when a bonded magnet is manufactured from these magnetic powders.
Accordingly, the object of the present invention is to provide a ribbon shaped magnet material, magnetic powder and rare earth bonded magnet that are able to provide a highly reliable magnet having excellent magnetic characteristics.
(1) A first ribbon shaped magnet material according to the present invention is obtained by allowing a molten liquid of an alloy containing rare earth elements and transition metals to contact a cooling member, the microstructure comprising a composite microstructure having soft magnetic phases and hard magnetic phases, wherein D1h, D1s, D2h and D2s satisfy the following equations:
D1s/D1hxe2x89xa60.9xe2x80x83xe2x80x83[1]
D2s/D2hxe2x89xa60.8xe2x80x83xe2x80x83[2]
where D1h denotes a mean grain size of the hard magnetic phase in the vicinity of a first surface as a surface that has been in contact with the cooling member, D1s denotes a mean grain size of the soft magnetic phase in the vicinity of the first surface, D2h denotes a mean grain size of the hard magnetic phase in the vicinity of a second surface as an opposed surface to the first surface, and D2s denotes a mean grain size of the soft magnetic phase in the vicinity of the second surface.
(2) The ribbon shaped magnet material preferably satisfies at least one of the equations [3] and [4]:
0.5xe2x89xa6D1h/D2hxe2x89xa61xe2x80x83xe2x80x83[3]
0.5xe2x89xa6D1s/D2sxe2x89xa61xe2x80x83xe2x80x83[4]
(3) A second ribbon shaped magnet material according to the present invention is obtained by allowing a molten liquid of an alloy containing rare earth elements and transition metals to contact a cooling member, the microstructure comprising a composite microstructure having soft magnetic phases and hard magnetic phases, wherein D1h, D1s, D2h and D2s satisfy the following equations:
0.5xe2x89xa6D1h/D2hxe2x89xa61xe2x80x83xe2x80x83[3]
xe2x80x830.5xe2x89xa6D1s/D2sxe2x89xa61xe2x80x83xe2x80x83[4]
where D1h denotes a mean grain size of the hard magnetic phase in the vicinity of a first surface as a surface that has been in contact with the cooling member, D1s denotes a mean grain size of the soft magnetic phase in the vicinity of the first surface, D2h denotes a mean grain size of the hard magnetic phase in the vicinity of a second surface as an opposed surface to the first surface, and D2s denotes a mean grain size of the soft magnetic phase in the vicinity of the second surface.
(4) Preferably, at least one of D1s and D2s is 75 nm or less.
(5) Preferably, at least one of D1h and D2h is 75 nm or less.
(6) D1h, D2h, D1s and D2s are preferably determined by measurements of X-ray diffraction.
(7) The alloy composition preferably contains B (boron)
(8) The alloy composition preferably contains Al (aluminum).
(9) Preferably, the alloy composition is represented by Rx(Fe1-yCoy)100-x-z-wBzAlw (wherein R denotes at least one of rare earth elements, and x is in the range of 7.1 to 9.9 atomic percentage (at %), y is in the range of 0 to 0.30, z is in the range of 4.6 to 6.8 at %, and w is in the range of 0.02 to 1.5 at %).
(10) R is preferably a rare earth element mainly comprising Nd and/or Pr.
(11) R includes Pr with a preferable proportion of 5 to 75% relative to the total content of R.
(12) R includes Dy with a preferable proportion of 14% or less relative to the total content of R.
(13) Preferably, the ribbon shaped magnet material is subjected to a heat treatment after contacting the cooling member.
(14) It is preferable that the cooling member is a cooling roll.
(15) The magnetic powder according to the present invention is obtained by pulverizing the ribbon shaped magnet material.
(16) Preferably, at least one time of heat treatment is applied to the magnetic powder in the manufacturing process or after manufacturing.
(17) The magnetic powder preferably has a mean particle size of 0.5 to 150 xcexcm.
(18) The rare earth bonded magnet is prepared by bonding the magnetic powder with a binding resin.
(19) Preferably, the rare earth bonded magnet contains 75 to 95.5 wt % of the magnetic powder.
(20) It is preferable that the rare earth bonded magnet has a coercive force HCJ of 320 to 720 kA/m.
(21) It is preferable that the rare earth bonded magnet has a magnetic energy product (BH)max of 60 kJ/m2.
(22) It is preferable that the rare earth bonded magnet has an absolute value of the irreversible flux loss (initial flux loss) of 5.7% or less.
(23) Preferably, the rare earth bonded magnet is subjected to multipolar magnetization or magnetized as a multipolar magnet.
(24) Preferably, the rare earth bonded magnet is used for a motor.